Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers.
Level 3 - non-randomized controlled study
Controlled parallel-group intervention trial (randomization not stated in abstract)
PubMed 28012184 · doi:10.1113/JP273230
What was done
Twenty-nine elite race walkers completed 3 weeks of intensified training with mild energy deficit while adhering to one of three isoenergetic diets: high carbohydrate availability (HCHO, n = 9; 8.6 g/kg/day carbohydrate, 2.1 g/kg/day protein, 1.2 g/kg/day fat), periodised carbohydrate availability (PCHO, n = 10; identical macronutrients alternating between low and high carbohydrate availability), or a ketogenic low-carbohydrate, high-fat diet (LCHF, n = 10; < 50 g/day carbohydrate, 78% energy from fat, 2.1 g/kg/day protein). Pre- and post-intervention tests evaluated VO2 peak, fat oxidation rates, exercise economy at roughly 20 km race pace, and 10-km race walk performance.
What was found
VO2 peak during race walking increased in all groups (P < 0.001, 90% CI: 2.55% to 5.20%). The LCHF group achieved peak fat oxidation rates of 1.57 +/- 0.32 g/min during 2 hours of walking at approximately 80% VO2 peak. Oxygen uptake as a percentage of new VO2 peak at 20 km race pace decreased in HCHO (90% CI: -7.047% to -2.55%) and PCHO (90% CI: -5.18% to -0.86%), but remained at pre-intervention levels in LCHF. Race times for 10 km improved by 6.6% (90% CI: 4.1% to 9.1%) in HCHO and 5.3% (90% CI: 3.4% to 7.2%) in PCHO, compared to no improvement (-1.6%, 90% CI: -8.5% to 5.3%) in LCHF.
Why it matters
This study shows that while a ketogenic diet markedly boosts whole-body fat oxidation and aerobic capacity, it increases oxygen cost at race velocities and negates the performance benefits of intensified training in elite endurance athletes.
Limits
The sample size was small (n = 29 across three groups), the intervention was limited to 3 weeks, and the abstract does not indicate whether dietary allocation was randomized. Findings in elite race walkers may not extrapolate to recreational athletes, other sports, or longer adaptation periods.
Cited by
- supports Studies by Louise Burke and John Hawley found a 2% performance decline in elite race walkers on a low-carbohydrate diet lasting 5 days to 3 weeks.